Basal vs. luminal A breast cancer subtypes: a matched case-control study using estrogen receptor, progesterone receptor, and HER-2 as surrogate markers.

Breast cancer is a heterogeneous disease that encompasses several distinct entities with different biological characteristics and clinical behavior. Basal subtype is considered as a prognostically unfavorable subset. The purpose of this study is to compare the clinico-pathological characteristics and outcome of basal vs. luminal A subtype, as approximated by ER, PR, and HER-2. Sixty-four patients with basal breast cancer were matched for age, stage, and year of diagnosis with 64 patients having luminal A disease. Basal tumors were immunohistochemically defined by a lack of expression of estrogen receptor (ER), progesterone receptor (PR), and HER-2, while luminal A cancers were ER+ or PR+, and HER-2-. As compared with luminal A, basal subtype patients had significantly larger primary tumor size, higher percentage of grade III tumor, more tumor that showed lymphovascular invasion, less presence of non-invasive disease, and higher proportion of extranodal extension. There was no statistically significant difference in metastatic sites, pathology type, or in the axillary lymph nodal status. A few patients received neoadjuvant chemotherapy--13 and 9 patients in basal and luminal A groups, respectively). The complete pathological response was 20% and 14%, respectively (not significant). At a median follow-up of approximately 2 years, there was no statistically significant difference in the overall survival rate between basal and luminal A patients. Analysis of disease-free survival (DFS) for stage I-III (53 patients in each group) showed that the median DFS for basal patients was 41.4 months (95% CI, 26.5-55.3 months), whereas the DFS for the luminal A patients was not reached (P = 0.014). After adjusting for several significant prognostics variables identified in a univariate analysis, a multivariate conditional logistic regression analysis identified the negative effect of lymphovascular invasion and the favorable influence of the use of neoadjuvant and/or adjuvant chemotherapy. This matched case-control study confirmed the poor clinical and pathological characteristics of patients with basal subtype and their unfavorable outcome compared with luminal A disease. Management of basal tumors remains a challenging task, and new therapeutic strategies are warranted.